This invention relates to roof curbs or cants, and in particular to an improved metal roof curb having inner and outer walls both of which perform the load bearing function. The invention also pertains to a novel method and apparatus for forming the linear form for the roof curb.
Roof curbs are used to support equipment mounted upon the flat roofs of industrial or commercial buildings. The curb, when fabricated into a structure of desired configuration, is used to support equipment, such as ventilating or exhaust air blowers, at a position spaced above the level of the roof to avoid penetration and damage by snow or water that may accumulate in sufficient depth upon the roof to reach the equipment or overflow into the interior of the building.
A roof curb structure is typically fabricated from an elongated linear form which is cut and mitered as required, with the cut portions of the linear form preferably being welded to one another. The linear forms can also be used as such as cant strips or wall cants, including horizontal expansion joint system with a suitable cap or cover adapted to accommodate expansion or contraction of the expansion joint. An endless variety of roof curbs and cants can be created from the linear curb form.
Typical roof curbs of the prior art include a flat top member extending the length of the linear curb form. When the linear form is fabricated into a desired roof curb, normally by use of a press brake or similar apparatus, a wood nailer or the like is fastened to the metal top member. Roofing felt can be attached to the nailer, or the nailer can be used as a cushioning and fastening implement for the supported equipment.
In such known roof curbs, the inner portion of the curb which forms the interior of a fabricated support structure is left open, that is, there is no inner wall, while the outer curb portion is bent downwardly and then outwardly to form an outer wall. The bottom of the roof curb is either added as a separate strip of metal, or comprises an inwardly turned extension of the outer curb portion. In either case, the inner side of the curb is normally open and therefore non load-supporting. Support in addition to that provided by the outer curb portion is always desirable and often required. Thus, a wooden beam or similar support could be inserted into the roof curb to provide additional load support.
Since the purpose of the roof curb, as noted above, is to elevate and support equipment above a building roof, were the inner side of the curb not open, an inner wall could serve as an additional load bearing portion of the roof curb. However, the inner sides of the prior art roof curbs are normally open, apparently because it is beyond the capability of standard metal bending equipment to form the roof curb from a single strip of metal to provide an inner wall. The difficulty in metal bending occurs when trying to either press brake or roll form the roof curb linear form since, when an inner wall is formed, there is no direct access into the interior of the form, thus precluding the use of conventional press brake or roll forming equipment.